1. Field of the Invention
The invention relates to an alarm system for detecting a movement or a change in a field of view supervised by a television camera.
2. Description of the Prior Art
In German Published Patent Specification No. 22 55 876 there is disclosed a television-based alarm system wherein uniform brightness regions within the scene viewed by a television camera are suppressed. For this purpose the video signal produced by the television camera is taken through a resonance filter. The signal thus obtained is rectified and transferred to a capacitively coupled band-pass filter. The band-pass filter serves for eliminating very slow or very quick changes. Thereafter any resulting single variation indicates a scene variation in the supervised field of view and causes a signal to be emitted. The response reliability of such an alarm system is small because it reacts only to relatively large dynamic changes of scene. A further disadvantage is that the response sensitivity does not vary and cannot therefore be suited to the detection of different scenic events.
Furthermore there is disclosed in German Published Patent Specification No. 20 02 478 an arrangement for supervising objects with the use of a television camera, wherein there is connected to the television camera an amplitude filter combined with an electronic counter. Upon a prescribed count being exceeded an alarm is actuated. In this arrangement also the reliability of response is low. This is so primarily because it is not possible to adapt to alternating light conditions. Furthermore variable components such as brightness, structure, movement or direction of movement cannot be evaluated differentially.
It is an object of the invention to provide an improved television-based alarm system which has, or may be designed to have, a response sensitivity and response characteristic which can be varied.